Optical glass, optical element blank, and optical element

ABSTRACT

Provided is optical glass in which an amount of P2O5 is 10.0 to 40.0 mass %, an amount of TiO2 is 5.0 to 40.0 mass %, an amount of Nb2O5 is 20.0 to 60.0 mass %, an amount of K2O is 0.01 mass % or more, a total amount of Li2O, Na2O, K2O, MgO, CaO, ZnO, SrO, and BaO [Li2O+Na2O+K2O+MgO+CaO+ZnO+SrO+BaO] is 20.0 mass % or less, a total amount of TiO2 and Nb2O5[TiO2+Nb2O5] is 55.0 mass % or more, a mass ratio [K2O/(Li2O+Na2O+K2O)] between the amount of K2O, and a total amount of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is 0.5 or more, a mass ratio [(MgO+CaO+ZnO+SrO+BaO)/(Li2O+Na2O+K2O)] between a total amount of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO], and the total amount of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is 0.30 to 10.0, a mass ratio [TiO2/K2O] between the amount of TiO2 and the amount of K2O is 3.0 or more, and a mass ratio [(Li2O+Na2O+MgO+CaO+ZnO+SrO)/(K2O+BaO)] between a total amount of Li2O, Na2O, MgO, CaO, ZnO, and SrO [Li2O+Na2O+MgO+CaO+ZnO+SrO], and a total amount of K2O and BaO [K2O+BaO] is 0.8 or less.

TECHNICAL FIELD

The present invention relates to optical glass, an optical elementblank, and an optical element.

BACKGROUND ART

In recent years, with the progress of an augmented reality (AR)technology, for example, a goggle-type or an eyeglass-type displaydevice has been developed as an AR device. For example, a lens having ahigh refractive index and a low specific gravity is required for thegoggle-type display device, and a demand for glass applicable to thelens is increasing.

JP 2012-17261 A, JP 2013-212935 A, JP 2013-227197 A, and JP 2015-63460 Adisclose optical glass containing Ti and Nb as a high-refractive-indexoptical glass. However, it is estimated that the above optical glass hasa too large specific gravity relative to a refractive index to beemployed as the lens for the AR device.

Here, there is a demand for optical glass in which the specific gravityis reduced while maintaining the high refractive index.

-   [Patent Literature 1] JP 2012-17261 A-   [Patent Literature 2] JP 2013-212935 A-   [Patent Literature 3] JP 2013-227197 A-   [Patent Literature 4] JP 2015-63460 A

SUMMARY

The present invention has been made in consideration of suchcircumstances, and an object thereof is to provide optical glass and anoptical element in which a refractive index is high, and a specificgravity is relatively low.

The gist of the present invention is as follows.

-   -   (1) Optical glass,    -   wherein an amount of P₂O₅ is 10.0 to 40.0 mass %,    -   an amount of TiO₂ is 5.0 to 40.0 mass %,    -   an amount of Nb₂O₅ is 20.0 to 60.0 mass %,    -   an amount of K₂O is 0.01 mass % or more,    -   a total amount of Li₂O, Na₂O, K₂O, MgO, CaO, ZnO, SrO, and BaO        [Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is 20.0 mass % or less,    -   a total amount of TiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] is 55.0 mass % or        more,    -   a mass ratio [K₂O/(Li₂O+Na₂O+K₂O)] between the amount of K₂O,        and a total amount of Li₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is 0.5        or more,    -   a mass ratio [(MgO+CaO+ZnO+SrO+BaO)/(Li₂O+Na₂O+K₂O)] between a        total amount of MgO, CaO, ZnO, SrO, and BaO,        [MgO+CaO+ZnO+SrO+BaO] and the total amount of Li₂O, Na₂O, and        K₂O [Li₂O+Na₂O+K₂O] is 0.30 to 10.0,    -   a mass ratio [TiO₂/K₂O] between the amount of TiO₂ and the        amount of K₂O is 3.0 or more, and    -   a mass ratio [(Li₂O+Na₂O+MgO+CaO+ZnO+SrO)/(K₂O+BaO)] between a        total amount of Li₂O, Na₂O, MgO, CaO, ZnO, and SrO        [Li₂O+Na₂O+MgO+CaO+ZnO+SrO], and a total amount of K₂O and BaO        [K₂O+BaO] is 0.8 or less.    -   (2) The optical glass according to (1),    -   wherein a mass ratio        [(TiO₂+Nb₂O₅)/(SiO₂+B₂O₃+Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO)]        between the total amount of TiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] and a        total amount of SiO₂, B₂O₃, Li₂O, Na₂O, K₂O, MgO, CaO, ZnO, SrO,        and BaO [SiO₂+B₂O₃+Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is 2.65 or        more.    -   (3) An optical element blank comprising the optical glass        according to (1) or (2).    -   (4) An optical element comprising the optical glass according        to (1) or (2).

According to the present invention, it is possible to provide opticalglass and an optical element in which a refractive index is high and aspecific gravity is relatively low.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views illustrating a configuration of a head-mounteddisplay that uses a light guide plate as an aspect of the presentinvention; and

FIG. 2 is a side view schematically illustrating a configuration of thehead-mounted display that uses the light guide plate as an aspect of thepresent invention.

In the present invention and in this specification, a glass compositionis noted on the basis of oxides unless otherwise stated. Here,“oxide-based glass composition” represents a glass composition obtainedby conversion on the assumption that glass raw materials are totallydecomposed at the time of melting, and exist as oxides in glass. Thetotal amount of all glass components noted on the basis of oxides(excluding Sb (Sb₂O₃), Ce (CeO₂), and Sn (SnO₂) which are added as aclarification agent) is set to 100 mass %. Notation of the respectiveglass components conforms to custom, and is described as SiO₂, TiO₂, andthe like. The amount and the total amount of the glass components arebased on a mass unless otherwise stated, and “%” represents “mass %”.

The amount of a glass component can be measured by a known method, forexample, a method such as inductively coupled plasma atomic emissionspectroscopic analysis (ICP-AES) and inductively coupled plasma massspectrometry (ICP-MS). In addition, in this specification and thepresent invention, when the amount of a constituent component is 0%,this represents that the constituent component is substantially notcontained, and the component is allowed to be contained in anunavoidable impurity level.

In addition, in this specification, a refractive index represents arefractive index nd in a d-line of helium (wavelength: 587.56 nm) unlessotherwise stated.

In addition, an Abbe number vd is used as a value representing aproperty relating to dispersion, and is expressed by the followingExpression. Here, nF represents a refractive index at an F line of bluehydrogen (wavelength: 486.13 nm), and nC represents a refractive indexat a C line of red hydrogen (wavelength: 656.27 nm).

vd=(nd−1)/(nF−nC)

Hereinafter, optical glass according to an embodiment of the presentinvention will be described. In the optical glass according to thisembodiment, an amount of P₂O₅ is 10.0 to 40.0 mass %,

-   -   an amount of TiO₂ is 5.0 to 40.0 mass %,    -   an amount of Nb₂O₅ is 20.0 to 60.0 mass %,    -   an amount of K₂O is 0.01 mass % or more,    -   a total amount of Li₂O, Na₂O, K₂O, MgO, CaO, ZnO, SrO, and BaO        [Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is 20.0 mass % or less,    -   a total amount of TiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] is 55.0 mass % or        more,    -   a mass ratio [K₂O/(Li₂O+Na₂O+K₂O)] between the amount of K₂O,        and a total amount of Li₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is 0.5        or more,    -   a mass ratio [(MgO+CaO+ZnO+SrO+BaO)/(Li₂O+Na₂O+K₂O)] between a        total amount of MgO, CaO, ZnO, SrO, and BaO        [MgO+CaO+ZnO+SrO+BaO], and the total amount of Li₂O, Na₂O, and        K₂O [Li₂O+Na₂O+K₂O] is 0.30 to 10.0,    -   a mass ratio [TiO₂/K₂O] between the amount of TiO₂ and the        amount of K₂O is 3.0 or more, and    -   a mass ratio [(Li₂O+Na₂O+MgO+CaO+ZnO+SrO)/(K₂O+BaO)] between a        total amount of Li₂O, Na₂O, MgO, CaO, ZnO, and SrO        [Li₂O+Na₂O+MgO+CaO+ZnO+SrO], and a total amount of K₂O and BaO        [K₂O+BaO] is 0.8 or less. Hereinafter, respective requirements        will be described.

In the optical glass according to this embodiment, the amount of P₂O₅ is10.0 to 40.0%. An upper limit of the amount of P₂O₅ is preferably 38.0%,and more preferably, may be 35.0%, 33.0%, 30.0%, or 28.0%. In addition,a lower limit of the amount of P₂O₅ is preferably 13.0%, and morepreferably, may be 15.0%, 18.0%, or 20.0%.

P₂O₅ is a network forming component, and is an essential component forcontaining a large amount of highly dispersive component in the glass.When the amount of P₂O₅ is set to the above-described range, the desiredrefractive index may be easily obtained, and a melting temperature canbe controlled within an appropriate range.

In the optical glass according to this embodiment, the amount of TiO₂ is5.0% to 40.0%. An upper limit of the amount of TiO₂ is preferably 38.0%,and more preferably, may be 35.0%, 33.0%, 30.0%, 28.0%, or 25.0%. Inaddition, a lower limit of the amount of TiO₂ is preferably 8.0%, andmore preferably, may be 10.0%, 13.0%, 15.0%, or 18.0%.

TiO₂ greatly contributes to a high refractive index and a highdispersion. In addition, among high-refractive-index components, TiO₂contributes to a low specific gravity. When the amount of TiO₂ is set tothe above-described range, a high refractive index and a low specificgravity are compatible with each other, and chemical durability can beimproved. On the other hand, when the amount of TiO₂ is excessivelylarge, the melting temperature may rise, generation of crystals in glassmay be promoted in the course of obtaining optical glass by molding andslowly cooling molten glass, and transparency of glass tends to decrease(turbidity tends to occur). In addition, coloration may increase.

In the optical glass according to this embodiment, the amount of Nb₂O₅is 20.0% to 60.0%. An upper limit of the amount of Nb₂O₅ is preferably58.0%, and more preferably, may be 55.0%, 53.0%, 50.0%, or 48.0%. Inaddition, a lower limit of the amount of Nb₂O₅ is preferably 23.0%, andmore preferably, may be 25.0%, 28.0%, 30.0%, 33.0%, 35.0%, 38.0%, or40.0%.

Nb₂O₅ is a component that contributes to a high refractive index andhigh dispersion. In addition, when the amount of Nb₂O₅ is set to theabove-described range, thermal stability and the chemical durability ofglass can be improved. On the other hand, when the amount of Nb₂O₅ isexcessively large, the melting temperature of glass may rise, thethermal stability of glass may deteriorate, and coloration of glasstends to be enhanced. In addition, there is a concern that a specificgravity of glass may increase.

In the optical glass according to this embodiment, the amount of K₂O is0.01% or more. A lower limit of the amount of K₂O is preferably 0.05%,and more preferably, may be 0.1%, 0.5%, 1.0%, or 1.5%. An upper limit ofthe amount of K₂O is preferably 20.0%, and more preferably, may be15.0%, 10.0%, or 5.0%.

K₂O has an operation of lowering the melting temperature and improvingthe thermal stability of glass, and contributes a low specific gravity,but when the amount is excessively large, the desired refractive indexis less likely to be obtained.

In the optical glass according to this embodiment, the total amount ofLi₂O, Na₂O, K₂O, MgO, CaO, ZnO, SrO, and BaO[Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is 20.0% or less. An upper limit ofthe total amount is preferably 18.0%, and more preferably, may be 15.0%,13.0%, or 10.0%. In addition, a lower limit of the total amount ispreferably 0.5%, and more preferably, may be 1.0%, 1.5%, 2.0%, 2.5%,3.0%, 3.5%, 4.0%, or 4.5%. When the total amount[Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is within the above-described range,the melting temperature may be lowered, the thermal stability of glassmay be improved, and glass having the desired refractive index is likelyto be obtained.

In the optical glass according to this embodiment, the total amount ofTiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] is 55.0% or more. A lower limit of the totalamount is preferably 56.0%, and more preferably, may be 57.0%, 58.0%,59.0%, or 60.0%. In addition, an upper limit of the total amount ispreferably 80.0%, and more preferably, may be 78.0%, 75.0%, 73.0%, or70.0%. When the total amount [TiO₂+Nb₂O₅] is within the above-describedrange, a high refractive index may be obtained, and stability of glassmay be improved.

In the optical glass according to this embodiment, the mass ratio[K₂O/(Li₂O+Na₂O+K₂O)] between the amount of K₂O, and a total amount ofLi₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is 0.5 or more. A lower limit of thetotal amount is preferably 0.53, and more preferably, may be 0.55, 0.58,or 0.60. When the mass ratio is within the above-described range,stability of glass may be improved.

In the optical glass according to this embodiment, the mass ratio[(MgO+CaO+ZnO+SrO+BaO)/(Li₂O+Na₂O+K₂O)] between the total amount of MgO,CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO], and the total amount ofLi₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is 0.30 to 10.0. An upper limit ofthe mass ratio is preferably 9.5, and more preferably, may be 9.0, 8.5,8.0, 7.5, or 7.0. In addition, a lower limit of the mass ratio ispreferably 0.35, and more preferably, may be 0.40, 0.45, or 0.50. Whenthe mass ratio is within the above-described range, stability of glassmay be improved.

In the optical glass according to this embodiment, the mass ratio[TiO₂/K₂O]between the amount of TiO₂ and the amount of K₂O is 3.0 ormore. A lower limit of the mass ratio is preferably 3.5, and morepreferably, may be 4.0, 4.5, or 5.0. In addition, an upper limit of themass ratio is preferably 50.0, and more preferably, may be 40.0, 30.0,or 20.0. When the mass ratio is within the above-described range, thedesired refractive index may be easily obtained, and stability of glassmay be improved.

In the optical glass according to this embodiment, a mass ratio[(Li₂O+Na₂O+MgO+CaO+ZnO+SrO)/(K₂O+BaO)] between a total amount of Li₂O,Na₂O, MgO, CaO, ZnO, and SrO [Li₂O+Na₂O+MgO+CaO+ZnO+SrO], and a totalamount of K₂O and BaO [K₂O+BaO] is 0.8 or less. An upper limit of themass ratio is preferably 0.78, and more preferably, may be 0.75, 0.73,0, or 0.70. When the mass ratio is within the above-described range,stability of glass may be improved.

In the optical glass according to this embodiment, with regard toamounts and ratios of glass components, and properties, other than theabove, a non-limiting example will be described below.

The optical glass according to this embodiment substantially does notcontain fluorine (F). That is, in the optical glass according to thisembodiment, an anion component is mainly oxygen (O). When beingexpressed in mass % with respect to a total substance amount of glass onthe basis of oxides, the amount of F is preferably less than 1.0% inouter percentage, and more preferably in the order of 0.5% or less, 0.2%or less, and 0.1% or less in outer percentage.

Here, with regard to the F component, the “outer percentage” representsthat a substance amount of the F component is expressed as mass % whenall cation components constituting glass are assumed to be composed ofoxides bonded with oxygen in charge balance, and when a substance amountof the entirety of glass composed of the oxides is set to 100%.

In the optical glass according to this embodiment, an upper limit of theamount of SiO₂ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. The amount of SiO₂ may be 0%.

SiO₂ is a glass network forming component, and has an operation ofimproving the thermal stability, the chemical durability, and weatherresistance of glass, increasing viscosity of molten glass, and allowingthe molten glass to be easily molded. On the other hand, when the amountof SiO₂ is large, the desired refractive index is less likely to beobtained.

In the optical glass according to this embodiment, an upper limit of theamount of B₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. The amount of B₂O₃ may be 0%.

B₂O₃ is a glass network forming component. In addition, among glassnetwork forming components, B₂O₃ contributes to a high refractive index.When the amount of B₂O₃ is set to the above-described range, the meltingtemperature can be controlled to an appropriate range, and the thermalstability of glass can be improved. On the other hand, when the amountof B₂O₃ is excessively large, the high refractive index may be hindered,and devitrification resistance tends to be lowered.

In the optical glass according to this embodiment, an upper limit of theamount of Al₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. The amount of Al₂O₃ may be 0%.

Al₂O₃ is a glass component having an operation of improving the chemicaldurability and the weather resistance of glass, and can also beconsidered as a network forming component. On the other hand, when theamount of Al₂O₃ increases, the desired refractive index is less likelyto be obtained, and the melting temperature may rise, and thedevitrification resistance of glass may deteriorate. In addition, aglass transition temperature Tg may rise, and a problem such asdeterioration of the thermal stability is likely to occur.

In the optical glass according to this embodiment, an upper limit of theamount of Li₂O is preferably 15.0%, and more preferably, may be 10.0%,8.0%, 5.0%, or 3.0%. In addition, a lower limit of the amount of Li₂O ispreferably 0.01%, and more preferably, may be 0.02%, 0.03%, 0.04%, or0.05%. The amount of Li₂O may be 0%.

When the amount of Li₂O is set to the above-described range, the meltingtemperature can be lowered and a low specific gravity can be obtained,and thus the thermal stability of glass can be improved. In addition,Li₂O contributes to a high refractive index among alkali components. Onthe other hand, when the amount of Li₂O is excessively large, thedesired refractive index is less likely to be obtained, and there is aconcern that the thermal stability, the chemical durability, and theweather resistance may deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of Na₂O is preferably 15.0%, and more preferably, may be 10.0%,8.0%, 5.0%, or 3.0%. In addition, a lower limit of the amount of Na₂O ispreferably 0%. The amount of Na₂O may be 0%.

Na₂O has an operation of lowering the melting temperature and improvingthe thermal stability of glass, and contributes to a low specificgravity, but when the amount is excessively large, the desiredrefractive index is less likely to be obtained.

In the optical glass according to this embodiment, an upper limit of theamount of Cs₂O is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Cs₂O ispreferably 0%.

Cs₂O has an operation of lowering the melting temperature and improvingthe thermal stability of glass, and contributes to a low specificgravity, but when the amount increases, the desired refractive index isless likely to be obtained.

In the optical glass according to this embodiment, an upper limit of theamount of MgO is preferably 15.0%, and more preferably, may be 10.0%,8.0%, 5.0%, or 3.0%. In addition, the amount of MgO may be 0%. MgO is aglass component having an operation of lowering the melting temperatureof glass, and improving the thermal stability and the devitrificationresistance. However, when the amount of MgO increases, the desiredrefractive index is less likely to be obtained, and the thermalstability and the devitrification resistance of glass may deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of CaO is preferably 15.0%, and more preferably, may be 10.0%,8.0%, 5.0%, or 3.0%. In addition, the amount of CaO may be 0%. CaO is aglass component having an operation of lowering the melting temperatureof glass, and improving the thermal stability and the devitrificationresistance. However, when the amount of CaO increases, the desiredrefractive index is less likely to be obtained, and the thermalstability and the devitrification resistance of glass may deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of SrO is preferably 15.0%, and more preferably, may be 10.0%,8.0%, 5.0%, or 3.0%. In addition, a lower limit of the amount of SrO ispreferably 0%. SrO is a glass component having an operation of loweringthe melting temperature of glass, and improving the thermal stabilityand the devitrification resistance. However, when the amount of SrOincreases, the specific gravity may increase, the desired refractiveindex is less likely to be obtained, and the thermal stability and thedevitrification resistance of glass may deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of BaO is preferably 20.0%, and more preferably, may be 18.0%,15.0%, 13.0%, or 10.0%. In addition, a lower limit of the amount of BaOis preferably 0.1%, and more preferably, may be 0.5%, 1.0%, 2.0%, or3.0%. BaO is a glass component having an operation of lowering themelting temperature of glass, and improving the thermal stability andthe devitrification resistance. However, when the amount of BaOincreases, the specific gravity may increase, the desired refractiveindex is less likely to be obtained, and the thermal stability and thedevitrification resistance of glass may deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of ZnO is preferably 15.0%, and more preferably, may be 10.0%,8.0%, 5.0%, or 3.0%. In addition, a lower limit of the amount of ZnO ispreferably 0%. ZnO is a glass component having an operation of loweringthe melting temperature of glass, and improving the thermal stabilityand the devitrification resistance. However, when the amount of ZnOincreases, the specific gravity may increase, the desired refractiveindex is less likely to be obtained, and the thermal stability and thedevitrification resistance of glass may deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of ZrO₂ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of ZrO₂ ispreferably 0%. ZrO₂ is a glass component having an operation of raisingthe refractive index of glass, and improving the thermal stability andthe devitrification resistance. However, when the amount of ZrO₂ isexcessively large, the specific gravity may increase, the meltingtemperature may rise, and the thermal stability tends to deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of WO₃ is preferably 15.0%, and more preferably, may be 13.0%,10.0%, 8.0%, 5.0%, 3.0%, or 1.0%. The amount of WO₃ may be 0%. WO₃ is aglass component that raises a refractive index of glass. However, whenthe amount of WO₃ is excessively large, the specific gravity mayincrease, and the thermal stability tends to deteriorate.

In the optical glass according to this embodiment, an upper limit of theamount of Bi₂O₃ is preferably 20.0%, and more preferably, may be 15.0%,10.0%, 5.0%, 3.0%, or 1%. In addition, a lower limit of the amount ofBi₂O₃ may be 0%. Bi₂O₃ is a glass component that raises the refractiveindex of glass. On the other hand, when the amount of Bi₂O₃ increases,the coloration of glass may increase. In addition, a high specificgravity may be caused.

In the optical glass according to this embodiment, an upper limit of theamount of Ta₂O₅ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Ta₂O₅is preferably 0%. Ta₂O₅ is a glass component that raises the refractiveindex of glass. However, when the amount of Ta₂O₅ increases, thespecific gravity of glass may increase, the thermal stability of glassmay deteriorate, and the melting temperature of glass may rise.

In the optical glass according to this embodiment, an upper limit of theamount of La₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of La₂O₃is preferably 0%. La₂O₃ is a glass component that raises the refractiveindex of glass. However, when the amount of La₂O₃ increases, thespecific gravity of glass may increase, the thermal stability of glassmay deteriorate, and the melting temperature of glass may rise.

In the optical glass according to this embodiment, an upper limit of theamount of Y₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Y₂O₃ ispreferably 0%. Y₂O₃ is a glass component that raises the refractiveindex of glass. However, when the amount of Y₂O₃ increases, the specificgravity of glass may increase, the thermal stability of glass maydeteriorate, and the melting temperature of glass may rise.

In the optical glass according to this embodiment, an upper limit of theamount of Gd₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Gd₂O₃is preferably 0%. Gd₂O₃ is a glass component that raises the refractiveindex of glass. However, when the amount of Gd₂O₃ increases, thespecific gravity of glass may increase, the thermal stability of glassmay deteriorate, and the melting temperature of glass may rise.

In the optical glass according to this embodiment, an upper limit of theamount of Lu₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Lu₂O₃is preferably 0%. Lu₂O₃ is a glass component that raises the refractiveindex of glass. However, when the amount of Lu₂O₃ increases, thespecific gravity of glass may increase.

In the optical glass according to this embodiment, an upper limit of theamount of Yb₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Yb₂O₃is preferably 0%. Yb₂O₃ is a glass component that raises the refractiveindex of glass. However, when the amount of Yb₂O₃ increases, thespecific gravity of glass may increase.

In the optical glass according to this embodiment, an upper limit of theamount of GeO₂ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of GeO₂ ispreferably 0%. GeO₂ is a component that has an operation of raising arefractive index nd, and is very expensive component among glasscomponents which are typically used. Accordingly, from the viewpoint ofreducing the production cost of glass, it is preferable that the amountof GeO₂ is within the above-described range.

In the optical glass according to this embodiment, an upper limit of theamount of HfO₂ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of HfO₂ ispreferably 0%. HfO₂ is a component that has an operation of raising therefractive index nd and increasing the specific gravity, and isexpensive. Accordingly, from the viewpoint of reducing the productioncost of glass, it is preferable that the amount of HfO₂ is within theabove-described range.

In the optical glass according to this embodiment, an upper limit of theamount of In₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of In₂O₃is preferably 0%. In₂O₃ is a component that has an operation of raisingthe refractive index nd and increasing the specific gravity, and isexpensive. Accordingly, from the viewpoint of reducing the productioncost of glass, it is preferable that the amount of In₂O₃ is within theabove-described range.

In the optical glass according to this embodiment, an upper limit of theamount of Ga₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Ga₂O₃is preferably 0%. Ga₂O₃ is a component that has an operation of raisingthe refractive index nd and increasing the specific gravity, and isexpensive. Accordingly, from the viewpoint of reducing the productioncost of glass, it is preferable that the amount of Ga₂O₃ is within theabove-described range.

In the optical glass according to this embodiment, an upper limit of theamount of Sc₂O₃ is preferably 10.0%, and more preferably, may be 8.0%,5.0%, 3.0%, or 1.0%. In addition, a lower limit of the amount of Sc₂O₃is preferably 0%. Sc₂O₃ has an operation of raising the refractive indexnd, and increases the specific gravity. Accordingly, from the viewpointof reducing the specific gravity of glass, it is preferable that theamount of Sc₂O₃ is within the above-described range.

In the optical glass according to this embodiment, an upper limit of thetotal amount of P₂O₅, TiO₂, and Nb₂O₅[P₂O₅+TiO₂+Nb₂O₅] is preferably98.0%, and more preferably, may be 97.0%, 96.0%, or 95.0%. In addition,a lower limit of the total amount is preferably 70.0%, and morepreferably, may be 73.0%, 75.0%, 78.0%, or 80.0%. When the total amount[P₂O₅+TiO₂+Nb₂O₅] is within the above-described range, the meltingtemperature may be lowered, and the stability of glass may be improved.

In the optical glass according to this embodiment, an upper limit of thetotal amount of Li₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is preferably 20.0%,and more preferably, may be 15.0%, 10.0%, or 5.0%. A lower limit of thetotal amount is preferably 0.1%, and more preferably, may be 0.5%, 1.0%,1.5%, or 2.0%. When the total amount [Li₂O+Na₂O+K₂O] is set to theabove-described range, the thermal stability can be improved, and themelting temperature may be lowered. On the other hand, when the totalamount is excessively large, there is a concern that the chemicaldurability and the weather resistance may deteriorate. In addition,there is a concern that the refractive index may decrease.

In the optical glass according to this embodiment, an upper limit of thetotal amount of SrO and BaO [SrO+BaO] is preferably 30.0%, and morepreferably, may be 28.0%, 25.0%, 23.0%, 20.0%, 18.0%, or 15.0%. A lowerlimit of the total amount is preferably 0.1%, and more preferably, maybe 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%. Any of these components has anoperation of improving the thermal stability of glass. However, thetotal amount [SrO+BaO] increases, the specific gravity may increase.

In the optical glass according to this embodiment, an upper limit of thetotal amount of ZnO, SrO, and BaO [ZnO+SrO+BaO] is preferably 30.0%, andmore preferably, may be 28.0%, 25.0%, 23.0%, 20.0%, 18.0%, or 15.0%. Alower limit of the total amount is preferably 0.5%, and more preferably,may be 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%. Any of these components has anoperation of lowering the melting temperature of glass and improving thethermal stability. However, when the total amount [ZnO+SrO+BaO]increases, the specific gravity may increase, and a desired refractiveindex may not be obtained.

In the optical glass according to this embodiment, an upper limit of thetotal amount of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] ispreferably 30.0%, and more preferably, may be 28.0%, 25.0%, 23.0%,20.0%, 18.0%, or 15.0%. A lower limit of the total amount is preferably0.1%, and more preferably, may be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%.Any of these components has an operation of lowering the meltingtemperature of glass and improving the thermal stability. However, whenthe total amount [MgO+CaO+ZnO+SrO+BaO] increases, a desired refractiveindex may not be obtained.

In the optical glass according to this embodiment, an upper limit of thetotal amount of TiO₂, Nb₂O₅, WO₃, and Bi₂O₃[TiO₂+Nb₂O₅+WO₃+Bi₂O₃] ispreferably 80.0%, and more preferably, may be 78.0%, 75.0%, 73.0%, or70.0%. In addition, a lower limit of the total amount is preferably40.0%, and more preferably, may be 43.0%, 45.0%, 48.0%, 50.0%, 53.0%, or55.0%. When the total amount [TiO₂+Nb₂O₅+WO₃+Bi₂O₃] is set to theabove-described range, a high refractive index and high dispersibilitymay be obtained, the stability of glass may be improved.

In the optical glass according to this embodiment, an upper limit of amass ratio [P₂O₅/(P₂O₅+TiO₂+Nb₂O₅)] between the amount of P₂O₅ and thetotal amount of P₂O₅, TiO₂, and Nb₂O₅[P₂O₅+TiO₂+Nb₂O₅] is preferably0.40, and more preferably, may be 0.38, 0.35, 0.33, or 0.30. A lowerlimit of the mass ratio is preferably 0.15, and more preferably, may be0.18, 0.20, or 0.23. When the mass ratio is within the above-describedrange, a desired refractive index is likely to be obtained, and thestability of glass may be improved.

In the optical glass according to this embodiment, an upper limit of amass ratio [TiO₂/([Li₂O+Na₂O+K₂O])] between the amount of TiO₂ and thetotal amount of Li₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is preferably 30.0,and more preferably, may be 20.0, 15.0, 13.0, or 10.0. A lower limit ofthe mass ratio is preferably 1.0, and more preferably, may be 1.5, 2.0,2.5, or 3.0. In addition, when the mass ratio is within theabove-described range, a desired refractive index is likely to beobtained, and the stability of glass may be improved.

In the optical glass according to this embodiment, a mass ratio[BaO/([MgO+CaO+ZnO+SrO+BaO])] between the amount of BaO and the totalamount of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] ispreferably 0 or more, and more preferably, a lower limit of the massratio may be 0.1, 0.2, 0.3, 0.4, or 0.5. When the mass ratio is withinthe above-described range, the stability of glass may be improved.

In the optical glass according to this embodiment, an upper limit of amass ratio [TiO₂/(MgO+CaO+ZnO+SrO+BaO)] between the amount of TiO₂ andthe total amount of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] ispreferably 50.0, and more preferably, may be 45.0, 40.0, 35.0, 30.0, or20.0. A lower limit of the mass ratio is preferably 0.1, and morepreferably, may be 0.3, 0.5, 0.8, or 1.0. In addition, when the massratio is within the above-described range, a low specific gravity and adesired refractive index are likely to be obtained, and the stability ofglass may be improved.

In the optical glass according to this embodiment, an upper limit of amass ratio [TiO₂/(TiO₂+Nb₂O₅)] between the amount of TiO₂ and the totalamount of TiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] is preferably 0.60, and morepreferably, may be 0.58, 0.55, 0.53, or 0.50. In addition, a lower limitof the mass ratio is preferably 0.10, and more preferably, may be 0.13,0.15, 0.18, or 0.20. Any of TiO₂ and Nb₂O₅ is a glass component thatcontributes to a high refractive index and high dispersibility, butbecomes the cause for an increase in the specific gravity. TiO₂ furthercontributes to the high refractive index in comparison to Nb₂O₅ but isless likely to increase the specific gravity of glass. Accordingly, inthe embodiment of the present invention, when the mass ratio[TiO₂/(TiO₂+Nb₂O₅)] is set to the above-described range, an opticalglass in which the refractive index is high, the stability is high, andthe specific gravity is small may be obtained.

In the optical glass according to this embodiment, an upper limit of amass ratio [TiO₂/(TiO₂+Nb₂O₅+WO₃+Bi₂O₃)] between the amount of TiO₂ andthe total amount of TiO₂, Nb₂O₅, WO₃, and Bi₂O₃ is preferably 0.60, andmore preferably, may be 0.58, 0.55, 0.53, or 0.50. A lower limit of themass ratio is preferably 0.10, and more preferably, may be 0.13, 0.15,0.18, or 0.20. Any of TiO₂, Nb₂O₅, WO₃, and Bi₂O₃ is a glass componentthat contributes to a high refractive index and high dispersibility, butbecomes the cause for an increase in the specific gravity. TiO₂ furthercontributes to the high refractive index in comparison to Nb₂O₅, WO₃,and Bi₂O₃, and is less likely to increases the specific gravity ofglass. Accordingly, in the embodiment of the present invention, whenmass ratio [TiO₂/(TiO₂+Nb₂O₅+WO₃+Bi₂O₃)] is set to the above-describedrange, an optical glass in which the refractive index is high, thestability is high, and the specific gravity is small may be obtained.

In the optical glass according to this embodiment, an upper limit of amass ratio [TiO₂/Nb₂O₅] between the amount of TiO₂ and the amount ofNb₂O₅ is preferably 2.0, and more preferably, may be 1.8, 1.5, 1.3, 1.0,or 0.8. In addition, a lower limit of the mass ratio is preferably 0.10,and more preferably, may be 0.13, 0.15, 0.18, or 0.20. Any of TiO₂ andNb₂O₅ is a glass component that contributes a high refractive index andhigh dispersibility, but becomes the cause for an increase in thespecific gravity. TiO₂ further contributes to the high refractive indexin comparison to Nb₂O₅, and is less likely to increase the specificgravity of glass. Accordingly, in the embodiment of the presentinvention, when the mass ratio [TiO₂/Nb₂O₅] is set to theabove-described range, an optical glass in which the refractive index ishigh, the stability is high, and the specific gravity is small may beobtained.

In the optical glass according to this embodiment, an upper limit of amass ratio [TiO₂/(Nb₂O₅+WO₃+Bi₂O₃)] between the amount of TiO₂ and thetotal amount of Nb₂O₅, WO₃, and Bi₂O₃ is preferably 2.0, and morepreferably, may be 1.8, 1.5, 1.3, 1.0, or 0.8. A lower limit of the massratio is preferably 0.10, and more preferably, may be 0.13, 0.15, 0.18,or 0.20. Any of TiO₂, Nb₂O₅, WO₃, and Bi₂O₃ is a glass component thatcontributes a high refractive index and high dispersibility, but becomesthe cause for an increase in the specific gravity. TiO₂ furthercontributes to the high refractive index in comparison to Nb₂O₅, WO₃,and Bi₂O₃, and is less likely to increase the specific gravity of glass.Accordingly, in the embodiment of the present invention, when the massratio [TiO₂/(Nb₂O₅+WO₃+Bi₂O₃)] is set to the above-described range, anoptical glass in which the refractive index is high, the stability ishigh, and the specific gravity is small may be obtained.

In the optical glass according to this embodiment, an upper limit of amass ratio [(TiO₂+Nb₂O₅)/(SiO₂+B₂O₃+Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO)]between the total amount of TiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] and the totalamount of SiO₂, B₂O₃, Li₂O, Na₂O, K₂O, MgO, CaO, ZnO, SrO, and BaO[SiO₂+B₂O₃+Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is preferably 20.0, andmore preferably, may be 18.0, 15.0, 13.0, or 10.0. A lower limit of themass ratio is preferably 0.5, and more preferably, may be 1.0, 1.5, 2.0,2.5, 2.65, or 3.0. When the mass ratio[(TiO₂+Nb₂O₅)/(SiO₂+B₂O₃+Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO)] set to theabove-described range, an optical glass in which the refractive index ishigh and the stability is high may be obtained.

<Other Component Compositions>

Any of Pb, As, Cd, Tl, Be, Se, and Te have toxicity. Therefore, it ispreferable that the optical glass according to this embodiment does notcontain these elements as a glass component.

Any of U, Th, and Ra is a radioactive element. Therefore, it ispreferable that the optical glass according to this embodiment does notcontain these elements as a glass component.

V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tmincrease coloration of glass, and may become a generation source offluorescence. Therefore, it is preferable that the optical glassaccording to this embodiment does not contain these elements as a glasscomponent.

Sb (Sb₂O₃), Ce (CeO₂), and Sn (SnO₂) are elements which function as aclarification agent and can be arbitrarily added. Among these, Sb(Sb₂O₃) is a clarification agent having a high clarification effect. Theclarification effect of Ce (CeO₂) is lower than that of Sb (Sb₂O₃). Whena large amount of Ce (CeO₂) is added, coloration of glass tends toincrease.

Note that, in this specification, the amounts of Sb (Sb₂O₃), Ce (CeO₂),and Sn (SnO₂) are expressed in outer percentage, and are not included inthe total amount of all glass components expressed on the basis ofoxides. That is, in this specification, the total amount of all glasscomponents except for Sb (Sb₂O₃), Ce (CeO₂), and Sn (SnO₂) is set to 100mass %.

The amount of Sb₂O₃ is expressed in outer percentage. That is, when thetotal amount of all glass components except for Sb₂O₃, CeO₂, and SnO₂ isset to 100 mass %, the amount of Sb₂O₃ is preferably 1.0% or less, andmore preferably in the order of 0.5% or less, 0.1% or less, 0.08% orless, 0.06% or less, 0.04% or less, and 0.02% or less. The amount ofSb₂O₃ may be 0%.

The amount of CeO₂ is also expressed in outer percentage. That is, whenthe total amount of all glass components except for Sb₂O₃, CeO₂, andSnO₂ is set to 100 mass %, the amount of CeO₂ is preferably 2.0% orless, and more preferably in the order of 1.0% or less, 0.5% or less,and 0.1% or less. The amount of CeO₂ may be 0%. When the amount of CeO₂is set to the above-described range, a clarification property of glasscan be improved.

The amount of SnO₂ is also expressed in outer percentage. That is, whenthe total amount of all glass components except for Sb₂O₃, CeO₂, andSnO₂ is set to 100 mass %, the amount of SnO₂ is preferably 2.0% orless, and more preferably in the order of 1.0% or less, 0.5% or less,and 0.1% or less. The amount of SnO₂ may be 0%. When the amount of SnO₂is set to the above-described range, the clarification property of glasscan be improved.

<Properties of Glass>

The optical glass according to this embodiment satisfies theabove-described composition, has a property of a low specific gravityeven though a refractive index is high, and preferably has the followingproperties.

(Refractive Index) In the optical glass according to this embodiment, arefractive index nd is 1.950 or more. A lower limit of the refractiveindex nd is preferably 1.955, and more preferably, may be 1.960, 1.965,1.970, 1.975, or 1.980. In addition, an upper limit of the refractiveindex nd is preferably 2.300, and more preferably, may be 2.250, 2.200,2.150, 2.100, or 2.050.

(Abbe Number) In the optical glass according to this embodiment, a lowerlimit of an Abbe number vd for obtaining desired dispersibility ispreferably 15.0, and more preferably, may be 15.5, 16.0, or 16.5. Inaddition, an upper limit of the Abbe number vd is preferably 20.0, andmore preferably, may be 19.5, 19.0, 18.5, or 18.0.

(Specific Gravity)

The optical glass according to this embodiment is high-refractive-indexglass, and the specific gravity is not large. When the specific gravityof glass can be reduced, the weight of a lens can be reduced. On theother hand, when the specific gravity is excessively small,deterioration of the thermal stability may be caused.

Accordingly, in the optical glass according to this embodiment, an upperlimit of the specific gravity is preferably 4.20, and more preferably,may be 4.15, 4.10, 4.05, 4.00, 3.95, 3.90, 3.85, or 3.80.

(Ratio Between Refractive Index Nd and Specific Gravity d)

In the optical glass according to this embodiment, a lower limit of aratio (nd/d) between the refractive index nd and the specific gravity dis preferably 0.48, and more preferably, may be 0.49, 0.50, 0.51, or0.52. An upper limit of the ratio (nd/d) is preferably 0.60, and morepreferably, may be 0.59, 0.58, or 0.57. When the refractive index nd andthe specific gravity d satisfy the above-described range, an opticalglass in which the refractive index is high and the specific gravity isrelatively reduced may be obtained.

(Glass Transition Temperature Tg)

In the optical glass according to this embodiment, an upper limit of aglass transition temperature Tg is preferably 800° C. from the viewpointof lowering a slow cooling temperature of glass, a heating and softeningtemperature, or a pressing temperature, and more preferably, may be 780°C., 750° C., 730° C., or 700° C. A lower limit of the glass transitiontemperature Tg is not particularly limited, but the lower limit istypically 380° C. Note that, from the viewpoint of suppressing cracks ofglass by further strengthening a glass network structure, or from theviewpoint of decreasing thermal expansion of glass and enhancing heatresistance of glass, a lower limit of the glass transition temperatureTg is preferably 390° C., and more preferably, may be 400° C., 410° C.,420° C., 430° C., or 440° C. Particularly, to enhance the heatresistance of glass having a high refractive index, a lower limit of theglass transition temperature Tg is preferably set to 460° C., and morepreferably, may be 480° C., 500° C., 510° C., 520° C., 530° C., or 535°C. The glass transition temperature Tg can be controlled by mainlyadjusting the amounts of Li, Na, and K or the total amount thereof, theamount of Zn, or the like.

(Degrees of Coloration λ70 and λ5)

A light beam transmitting property of the optical glass according tothis embodiment can also be evaluated by the degrees of coloration λ70and λ5.

With respect to a glass sample having a thickness of 10.0 mm±0.1 mm, aspectral transmittance is measured in a wavelength range of 200 to 700nm, a wavelength at which an external transmittance is 70% is set asλ70, and a wavelength at which the external transmittance is 5% is setas λ5.

An upper limit of λ70 of the optical glass according to this embodimentis preferably 650 nm, and more preferably, may be 640 nm, 630 nm, 620nm, 610 nm, or 600 nm. An upper limit of λ5 is preferably 450 nm, andmore preferably, may be 440 nm, 430 nm, 420 nm, 410 nm, or 400 nm.

<Production of Optical Glass>

The optical glass according to the embodiment of the present inventionmay be prepared by combining glass raw materials to be theabove-described predetermined refractive index and composition, and byusing the combined glass raw materials in accordance with a known glassproduction method. For example, a plurality of kinds of compounds arecombined and are sufficiently mixed to obtain a batch raw material, andthe batch raw material is put into a quartz crucible or a platinumcrucible and is roughly melted. The molten product obtained by the roughmelting is quickly cooled and is pulverized to prepare a cullet.Furthermore, the cullet is put into a platinum crucible, and is heatedand remelted to obtain molten glass. The molten glass is molded afterclarification and homogenization, and is slowly cooled to obtain anoptical glass. In the molding and slow cooling of the molten glass, aknown method may be applicable.

Note that, compounds which are used when combining the batch rawmaterial are not particularly limited as long as desired glasscomponents can be introduced into the glass to be desired amounts, butexamples of the compounds include oxides, carbonates, nitrates,hydroxides, fluorides, and the like.

<Production of Optical Element or the Like>

A known method may be applicable for producing an optical element byusing the optical glass according to the embodiment of the presentinvention. For example, glass raw materials are melted to obtain moltenglass, and the molten glass is cast into a mold and is molded into aplate shape, thereby preparing a glass material including the opticalglass according to the present invention. The obtained glass material isappropriately cut, grinded, and polished to prepare a cut piece having asize and a shape suitable for press molding. The cut piece is heated,softened, and press molded (reheat press) by a known method, therebypreparing an optical element blank that approximates a shape of theoptical element. The optical element blank is annealed, and is grindedand polished by a known method, thereby preparing an optical element.

An optical functional surface of the prepared optical element may becoated with an antireflection film, a total reflection film, or the likein correspondence with the purpose of use.

According to an aspect of the present invention, an optical elementincluding the optical glass can be provided. Examples of the kind of theoptical element include a lens such as a planar lens, spherical lens,and an aspherical lens, a prism, a diffraction grating, a light guideplate, and the like. Examples of a shape of the lens include variousshapes such as a biconvex lens, a plano-convex lens, a biconcave lens, aplano-concave lens, a convex meniscus lens, and a concave meniscus lens.Examples of the application of the light guide plate include displaydevices such as eyeglass-type device in an augmented reality (AR)display type, an eyeglass-type device in a mixed reality (MR) displaytype, and the like. The light guide plate is plate-shaped glass that isattached to a frame of the eyeglass-type device, and includes theoptical glass. A diffraction grating configured to change an advancingdirection of a light beam that propagates through the inside of thelight guide plate while repeating total reflection may be formed on asurface of the light guide plate as necessary. The diffraction gratingcan be formed by a known method. When wearing the eyeglass-type deviceincluding the light guide plate, the light beam that propagates throughthe inside of the light guide plate is incident on pupils, and afunction of augmented reality (AR) display or mixed reality (MR) displaycan be exhibited. The eyeglass-type device is disclosed, for example, inJP Patent Application Laid Open (Translation of PCT Application) No.2017-534352, and the like. Note that, the light guide plate can beprepared by a known method. The optical element can be produced by amethod including a process of processing a glass molded body includingthe optical glass. Examples of the processing include severing, cutting,rough grinding, fine grinding, polishing, and the like. At the time ofperforming the processing, if the glass according to the presentinvention is used, breakage can be reduced, and a high-quality opticalelement can be stably supplied.

<Image Display Device>

A light guide plate that is an aspect of the present invention, and animage display device using the light guide plate will be described indetail with reference to the accompanying drawings. Note that, the samereference numeral will be given the same or equivalent portion, anddescription thereof will not be repeated.

FIGS. 1A and 1B are views illustrating a configuration of a head-mounteddisplay 1 (hereinafter, abbreviated as “HMD 1”) using a light guideplate 10 that is an aspect of the present invention. FIG. 1A is a frontside perspective view of the HMD 1, and FIG. 1B is a rear sideperspective view of the HMD 1. As illustrated in FIG. 1A and FIG. 1B, aneyeglass lens 3 is attached to a front portion of an eyeglass type frame2 mounted on the head of a user. A backlight 4 that illuminates an imageis attached to an attachment portion 2 a of the eyeglass type frame 2. Asignal processing device 5 that projects an image and a speaker 6 thatreproduces a voice are provided in a temple portion of the eyeglass typeframe 2. A flexible printed circuit (FPC) 7 that constitutes aninterconnection led-out from a circuit of the signal processing device 5is wired to the eyeglass type frame 2. A display element unit (forexample, a liquid crystal display element) 20 is wired to the centralposition of user's eyes by the FPC 7, and is held so that approximatelythe central portion of the display element unit 20 is disposed on anoptical axial line of the backlight 4. The display element unit 20 isrelatively fixed to a light guide plate 10 to be located atapproximately the central portion of the light guide plate 10. Inaddition, holographic optical elements (HOEs) 32R and 32L (first opticalelements) are tightly fixed onto a first surface 10 a of the light guideplate 10 at sites in front of user' eyes by adhesion or the like. HOEs52R and 52L are staked on a second surface 10 b of the light guide plate10 at a position facing the display element unit 20 with the light guideplate 10 interposed therebetween.

FIG. 2 is a side view schematically illustrating the configuration ofthe HMD 1 that is an aspect of the present invention. Note that, in FIG.2 , only main parts of an image display device are illustrated forclarifying the drawing, and illustration of the eyeglass type frame 2and the like is omitted. As illustrated in FIG. 2 , the HMD 1 has astructure that is laterally symmetric to a central line X connecting thecenter of an image display element 24 and the center of the light guideplate 10. In addition, light beams of respective wavelengths which areincident from the image display element 24 onto the light guide plate 10are divided into two parts to be guided to a right eye and a left eye ofa user, respectively, as to be described later. Optical paths of thelight beams of respective wavelengths which are guided to the eyes arealso approximately laterally symmetric to the central line X.

As illustrated in FIG. 2 , the backlight 4 includes a laser light source21, a diffusion optical system 22, and a microlens array 23. The displayelement unit 20 is an image generation unit including the image displayelement 24, and is driven, for example, in a field sequential method.The laser light source 21 includes laser light sources corresponding torespective wavelengths of R (wavelength: 436 nm), G (wavelength: 546nm), and B (wavelength: 633 nm), and sequentially emits light beams ofrespective wavelengths at a high speed. The light beams of respectivewavelengths are incident on the diffusion optical system 22 and themicrolens array 23, are converted into a uniform high-directivityparallel luminous flux without unevenness in a light quantity, and arevertically incident on a display panel surface of the image displayelement 24.

For example, the image display element 24 is a transmissive liquidcrystal (LCDT-LCOS) panel that is driven in a field sequential type. Theimage display element 24 modulates light beams of respective wavelengthsin correspondence with an image signal that is generated by an imageengine (not illustrated) of the signal processing device 5. The lightbeams of respective wavelengths which are modulated in a pixel of aneffective region of the image display element 24 are incident on thelight guide plate 10 with a predetermined luminous flux cross-section(approximately the same shape as in the effective region). Note that,for example, the image display element 24 may be substituted with adifferent type display element such as a digital mirror device (DMD),reflective liquid crystal (LCOS) panel, micro electro mechanical systems(MEMS), organic electro-luminescence (EL), and inorganic EL.

Note that, the display element unit 20 may be set as an image generationunit of a simultaneous display element (a display element including apredetermined array of RGB color filters on the front surface of anemission surface) without limitation to the field sequential typedisplay element. In this case, as the light source, for example, a whitelight source is used.

As illustrated in FIG. 2 , light beams of respective wavelengths whichare modulated by the image display element 24 are sequentially incidenton the inside of the light guide plate 10 from the first surface 10 a.HOEs 52R and 52L (second optical elements) are stacked on the secondsurface 10 b of the light guide plate 10. For example, the HOEs 52R and52L are rectangular reflective volume phase type HOEs, and have aconfiguration obtained by stacking three sheets of photopolymers on eachof which interference fringes corresponding to light beams of respectivewavelengths of R, G, and B are recorded. That is, the HOEs 52R and 52Lare configured to have a wavelength selection function of diffractingthe light beams of respective wavelengths of R, G, and B, andtransmitting the light beams of the other wavelengths.

Note that, the HOEs 32R and 32L are also reflective volume phase typeHOEs, and have the same layer structure as in the HOEs 52R and 52L. Inthe HOEs 32R and 32L and the HOEs 52R and 52L, for example, pitches ofinterference fringe patterns may be approximately the same as eachother.

The HOEs 52R and 52L are concentric to each other and are stacked in astate in which the interference fringe patterns are inverted by 180(deg). In addition, the HOEs 52R and 52L are tightly fixed onto thesecond surface 10 b of the light guide plate 10 by adhesion or the likeso that the centers thereof match the central line X in a stacked state.The light beams of respective wavelengths which are modulated by theimage display element 24 are sequentially incident on the HOEs 52R and52L through the light guide plate 10.

The HOEs 52R and 52L diffract light beams of respective wavelengthswhich are sequentially incident by applying a predetermined angle so asto guide the light beams to the right eye and the left eye. The lightbeams of respective wavelengths which are diffracted by the HOEs 52R and52L propagate through the inside of the light guide plate 10 whilerepeating total reflection at an interface between the light guide plate10 and the air, and are incident on the HOEs 32R and 32L. Here, the HOEs52R and 52L apply the same diffraction angle to light beams ofrespective wavelengths. Accordingly, light beams of all wavelengths ofwhich incident positions on the light guide plate 10 are approximatelythe same (or which are emitted from approximately the same coordinateswithin an effective region of the image display element 24 according toanother expression) propagate along approximately the same optical pathinside the light guide plate 10 and are incident on approximately thesame position on the HOEs 32R and 32L. According to another viewpoint,the HOEs 52R and 52L diffract light beams of respective wavelengths ofRGB so that a pixel positional relationship of an image displayed on theeffective region of the image display element 24 within the effectiveregion is reliably reproduced on the HOEs 32R and 32L.

As described above, according to the aspect of the present invention,each of the HOEs 52R and 52L diffracts light beams of all wavelengthsemitted from approximately the same coordinates in the effective regionof the image display element 24 to be incident on the approximately thesame position on each of the HOEs 32R and 32L. Alternatively, the HOEs52R and 52L may be configured to diffract light beams of allwavelengths, which constitute originally the same pixels relativelysifted within the effective region of the image display element 24, tobe incident on approximately the same position on the HOEs 32R and 32L.

The light beams of respective wavelengths which are incident onto theHOEs 32R and 32L are diffracted by the HOEs 32R and 32L and aresequentially emitted to the outside from the second surface 10 b of thelight guide plate 10 in an approximately vertical manner. The lightbeams of respective wavelengths which are emitted as approximatelyparallel light beams as described above are imaged on a right eye retinaand a left eye retina of a user as a virtual image I of an imagegenerated by the image display element 24. In addition, a condenseroperation may be applied to the HOEs 32R and 32L so that the user canobserve the virtual image I of an enlarged image. That is, as lightbeams are incident on a peripheral region of the HOEs 32R and 32L, thelight beams may be emitted at an angle to be close to the center of thepupil and may be imaged on a user's retina. Alternatively, in order toallow a user to observe the virtual image I of the enlarged image, theHOEs 52R and 52L may diffract light beams of respective wavelengths ofRGB so that a pixel positional relationship on the HOEs 32R and 32L hasa similar shape that is enlarged with respect to the pixel positionalrelationship of the image displayed on the effective region of the imagedisplay element 24 within the effective region.

Since the higher a refractive index is, the shorter an equivalentoptical path length in air of light beams propagating through the insideof the light guide plate 10 is, when using the optical glass having ahigh refractive index according to this embodiment, an apparent viewingangle with respect to a width of the image display element 24 can beenlarged. In addition, since the specific gravity is suppressed to below although the refractive index is high, a light guide plate that islight in weight and is capable of obtaining the above-described effectcan be provided.

Note that, the light guide plate that is an aspect of the presentinvention can be used in a see-through transmissive head-mounteddisplay, a non-transmissive head-mounted display, or the like.

In the head-mounted display, since the light guide plate includes theoptical glass having a high refractive index and a low specific gravityaccording to this embodiment, a sense of immersion due to a wide viewingangle is excellent. Accordingly, the head-mounted display is suitable asan image display device that is used in combination with an informationterminal, or that is used to provide augmented reality (AR) or the like,or to provide movie watching, gaming, virtual reality (VR), or the like.

Hereinbefore, description has been with reference to the head-mounteddisplay, but the light guide plate may be attached to other imagedisplay devices.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to examples. However, the present invention is not limited toaspects illustrated in the examples.

Example 1

Glass samples having glass compositions shown in Table 1 were preparedin the following procedure, and various evaluations were performed.Evaluation results are shown in Table 1.

[Preparation of Optical Glass]

Compound raw materials corresponding to constituent components of glass,that is, raw materials such as phosphates, carbonates, and oxides wereweighed, and were sufficiently mixed to obtain a combination rawmaterial. The combination raw material was put into a platinum crucibleand was heated and melted at 1000° C. to 1350° C. in the atmosphericatmosphere. The resultant melt was stirred to be homogenized andclarified, thereby obtaining molten glass. The molten glass was castinto a mold to be molded and was slowly cooled, thereby obtaining aglass sample having a block shape.

[Confirmation of Glass Component Composition]

With respect to the obtained glass sample, the amounts of respectiveglass components were measured by inductively coupled plasma atomicemission spectroscopic analysis (ICP-AES), and it was confirmed that theamounts satisfy respective compositions shown in Table 1. Note that, itwas confirmed that fluorine (F) is not contained in all glass samples.

[Measurement of Optical Properties]

With respect to the obtained glass samples, a specific gravity, arefractive index nd, an Abbe number vd, a glass transition temperatureTg, and the degrees of coloration λ70 and λ5 were measured by thefollowing methods.

[1] Specific Gravity

The specific gravity was measured by an Archimedes method.

[2] Refractive Index nd and Abbe Number vd

Refractive indexes nd, ng, nF, and nC were measured by a refractiveindex measuring method conforming to JIS B 7071-1, and the Abbe numbervd was calculated on the basis of the following Expression.

vd=(nd−1)/(nF−nC)

[3] Glass Transition Temperature Tg

The glass transition temperature Tg was measured by using a differentialscanning calorimeter (DSC3300SA) manufactured by NETZSCH Japan K.K. Asample was pulverized, the pulverized sample was weighed in a weightcorresponding to approximately 0.02 cc was measured, and the weighedsample was put into a Pt pan with a diameter of 5 mm. The measurementwas performed under conditions of a temperature increase rate of 10°C./min and a highest temperature of 1000° C. Alumina (Al₂O₃) was used asa standard sample.

[4] λ70, λ5

The sample was processed to have a thickness of 10 mm and to haveparallel and optically polished planar surfaces, and a spectraltransmittance in a wavelength region of 280 nm to 700 nm was measured.An intensity of light beams vertically incident on one of the opticallypolished planar surfaces was set as an intensity A, and an intensity oflight beams emitted from the other planar surface was set as anintensity B, thereby calculating a spectral transmittance B/A. Awavelength at which the spectral transmittance becomes 70% was set asλ70, and a wavelength at which the spectral transmittance becomes 5% wasset as λ5. Note that, a reflection loss of light beams on a samplesurface is also included in the spectral transmittance.

Results are shown in the following tables.

TABLE 1 Sample 1 2 3 4 5 6 7 8 9 10 P₂O₅ 24.79 22.97 22.51 23.35 24.4323.91 23.47 20.33 20.12 24.25 SiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 B₂O₃ 0.00 0.00 0.00 0.74 2.33 2.28 2.31 2.55 2.53 0.00Al₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li₂O 0.00 0.080.08 0.08 0.08 0.08 0.08 0.00 0.00 2.04 Na₂O 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 K₂O 4.20 3.90 3.82 3.96 3.10 3.03 4.12 1.741.73 2.68 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 CaO 0.001.17 0.00 0.00 1.25 0.00 0.00 0.00 0.00 0.00 SrO 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 BaO 3.26 0.00 3.15 3.26 0.00 3.34 1.7017.15 16.97 3.49 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00TiO₂ 25.54 21.85 21.42 23.06 24.13 23.62 23.96 11.97 10.25 14.55 Nb₂O₅31.15 39.09 38.31 36.90 35.65 34.89 35.40 46.25 48.41 52.98 ZrO₂ 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi₂O₃ 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 WO₃ 11.07 10.93 10.71 8.64 9.04 8.85 8.970.00 0.00 0.00 Y₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00La₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sb₂O₃ 0.00 0.200.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.20 100.20100.00 100.00 100.00 100.00 100.00 100.00 100.00 Li₂O + Na₂O + K₂O +7.45 5.15 7.04 7.31 4.43 6.45 5.89 18.89 18.69 8.22 MgO + CaO + ZnO +SrO + BaO TiO₂ + Nb₂O₅ 56.69 60.95 59.73 59.96 59.78 58.51 59.35 58.2258.66 67.53 K₂O/ 1.00 0.98 0.98 0.98 0.97 0.97 0.98 1.00 1.00 0.57(Li₂O + Na₂O + K₂O) (MgO + CaO + ZnO + 0.78 0.30 0.81 0.81 0.39 1.070.40 9.83 9.83 0.74 SrO + BaO)/ (Li₂O + Na₂O + K₂O) TiO₂/K₂O 6.08 5.615.61 5.82 7.79 7.79 5.82 6.86 5.94 5.43 (Li₂O + Na₂O + MgO + 0.00 0.320.01 0.01 0.43 0.01 0.01 0.00 0.00 0.33 CaO + ZnO + SrO)/ (K₂O + BaO) nd1.99414 2.01513 2.01533 2.00405 1.99186 1.99236 1.9919 1.98058 1.980632.00083 νd 16.56 16.4 16.42 16.62 16.82 16.85 16.76 18.72 18.76 17.38Specific gravity 3.649 3.683 3.74 3.671 3.565 3.624 3.593 3.925 3.9443.648 Tg 66 649 653 657 624 631 627 680 681 647 λ70 594 545 526 519 511510 513 491 491 518 λ5 408 412 412 405 404 404 404 392 392 396nd/specific gravity 0.55 0.55 0.54 0.55 0.56 0.55 0.55 0.50 0.50 0.55P₂O₅ + TiO₂ + Nb₂O₅ 81.47 83.92 82.24 83.31 84.21 82.42 82.82 78.5578.78 91.78 Li₂O + Na₂O + K₂O 4.20 3.98 3.90 4.04 3.18 3.11 4.20 1.741.73 4.72 SrO + BaO 3.26 0.00 3.15 3.26 0.00 3.34 1.70 17.15 16.97 3.49ZnO + SrO + BaO 3.26 0.00 3.15 3.26 0.00 3.34 1.70 17.15 16.97 3.49MgO + CaO + ZnO + 3.26 1.17 3.15 3.26 1.25 3.34 1.70 17.15 16.97 3.49SrO + BaO TiO₂ + Nb₂O₅ + 67.76 71.88 70.44 68.60 68.82 67.36 68.33 58.2258.66 67.53 WO₃ + Bi₂O₃ P₂O₅/ 0.30 0.27 0.27 0.28 0.29 0.29 0.28 0.260.26 0.26 (P₂O₅ + TiO₂ + Nb₂O₅) TiO₂/ 6.08 5.50 5.50 5.71 7.59 7.59 5.716.86 5.94 3.08 (Li₂O + Na₂O + K₂O) BaO/(MgO + CaO + 1.00 0.00 1.00 1.000.00 1.00 1.00 1.00 1.00 1.00 ZnO + SrO + BaO) TiO₂/(MgO + CaO + 7.8418.60 6.80 7.06 19.31 7.06 14.13 0.70 0.60 4.17 ZnO + SrO + BaO)TiO₂/(TiO₂ + Nb₂O₅) 0.45 0.36 0.36 0.38 0.40 0.40 0.40 0.21 0.17 0.22TiO₂/(TiO₂ + Nb₂O₅ + 0.38 0.30 0.30 0.34 0.35 0.35 0.35 0.21 0.17 0.22WO₃ + Bi₂O₃) TiO₂/Nb₂O₅ 0.82 0.56 0.56 0.62 0.68 0.68 0.68 0.26 0.210.27 TiO₂/(Nb₂O₅ + 0.60 0.44 0.44 0.51 0.54 0.54 0.54 0.26 0.21 0.27WO₃ + Bi₂O₃) (TiO₂ + Nb₂O₅)/ 7.60 11.83 8.48 7.45 8.85 6.70 7.23 2.712.76 8.22 (SiO₂ + B₂O₃ + Li₂O + Na₂O + K₂O + MgO + CaO + ZnO + SrO +BaO) Sample 11 12 13 14 15 16 17 18 19 20 P₂O₅ 20.95 20.28 24.85 20.6720.98 20.62 24.10 24.40 20.42 20.87 SiO₂ 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 B₂O₃ 2.63 2.55 0.00 2.60 2.64 1.88 0.00 0.00 2.212.26 Al₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li₂O 0.000.00 2.09 0.00 0.00 0.00 2.03 2.05 0.00 0.00 Na₂O 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 K₂O 1.80 1.74 2.75 1.45 1.96 2.40 2.672.70 1.90 1.95 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 CaO0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 SrO 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 BaO 11.31 10.95 3.58 13.51 11.3213.47 3.47 3.51 13.35 13.64 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 TiO₂ 15.65 10.34 18.64 14.77 15.40 14.73 13.56 15.56 12.9816.56 Nb₂O₅ 47.66 54.14 48.09 47.01 47.71 46.90 54.17 51.78 49.14 44.72ZrO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi₂O₃ 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 WO₃ 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 Y₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 La₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sb₂O₃0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Li₂O + Na₂O +K₂O + 13.11 12.69 8.42 14.95 13.28 15.88 8.17 8.27 15.25 15.59 MgO +CaO + ZnO + SrO + BaO TiO₂ + Nb₂O₅ 63.31 64.48 66.73 61.78 63.11 61.6367.73 67.34 62.11 61.28 K₂O/ 1.00 1.00 0.57 1.00 1.00 1.00 0.57 0.571.00 1.00 (Li₂O + Na₂O + K₂O) (MgO + CaO + ZnO + 6.29 6.29 0.74 9.345.79 5.61 0.74 0.74 7.01 7.01 SrO + BaO)/ (Li₂O + Na₂O + K₂O) TiO₂/K₂O8.70 5.94 6.78 10.21 7.87 6.13 5.09 5.77 6.81 8.51 (Li₂O + Na₂O + MgO +0.00 0.00 0.33 0.00 0.00 0.00 0.33 0.33 0.00 0.00 CaO + ZnO + SrO)/(K₂O + BaO) nd 2.00432 2.00525 2.00054 2.00144 2.00177 1.99907 2.000742.00084 2.00076 2.00005 νd 17.72 17.81 17.25 17.89 17.5 17.91 17.4 17.3517.94 17.85 Specific gravity 3.795 3.855 3.614 3.854 3.801 3.852 3.6613.639 3.868 3.84 Tg 654 675 637 671 649 672 647 641 667 671 λ70 517 51531 511 511 509 518 513 509 502 λ5 397 394 397 396 397 396 395 395 395397 nd/specific gravity 0.53 0.52 0.55 0.52 0.53 0.52 0.55 0.55 0.520.52 P₂O₅ + TiO₂ + Nb₂O₅ 84.26 84.76 91.58 82.45 84.09 82.24 91.83 91.7382.53 82.15 Li₂O + Na₂O + K₂O 1.80 1.74 4.84 1.45 1.96 2.40 4.70 4.751.90 1.95 SrO + BaO 11.31 10.95 3.58 13.51 11.32 13.47 3.47 3.51 13.3513.64 ZnO + SrO + BaO 11.31 10.95 3.58 13.51 11.32 13.47 3.47 3.51 13.3513.64 MgO + CaO + ZnO + 11.31 10.95 3.58 13.51 11.32 13.47 3.47 3.5113.35 13.64 SrO + BaO TiO₂ + Nb₂O₅ + 63.31 64.48 66.73 61.78 63.11 61.6367.73 67.34 62.11 61.28 WO₃ + Bi₂O₃ P₂O₅/ 0.25 0.24 0.27 0.25 0.25 0.250.26 0.27 0.25 0.25 (P₂O₅ + TiO₂ + Nb₂O₅) TiO₂/ 8.70 5.94 3.85 10.217.87 6.13 2.89 3.27 6.81 8.51 (Li₂O + Na₂O + K₂O) BaO/(MgO + CaO + 1.001.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 ZnO + SrO + BaO)TiO₂/(MgO + CaO + 1.38 0.94 5.21 1.09 1.36 1.09 3.91 4.43 0.97 1.21ZnO + SrO + BaO) TiO₂/(TiO₂ + Nb₂O₅) 0.25 0.16 0.28 0.24 0.24 0.24 0.200.23 0.21 0.27 TiO₂/(TiO₂ + Nb₂O₅ + 0.25 0.16 0.28 0.24 0.24 0.24 0.200.23 0.21 0.27 WO₃ + Bi₂O₃) TiO₂/Nb₂O₅ 0.33 0.19 0.39 0.31 0.32 0.310.25 0.30 0.26 0.37 TiO₂/(Nb₂O₅ + 0.33 0.19 0.39 0.31 0.32 0.31 0.250.30 0.26 0.37 WO₃ + Bi₂O₃) (TiO₂ + Nb₂O₅)/ 4.02 4.23 7.92 3.52 3.973.47 8.29 8.15 3.56 3.43 (SiO₂ + B₂O₃ + Li₂O + Na₂O + K₂O + MgO + CaO +ZnO + SrO + BaO)

TABLE 2 Sample 21 22 23 24 25 26 27 28 29 30 P₂O₅ 19.99 23.60 24.1224.71 24.77 24.67 23.89 26.66 25.97 25.42 SiO₂ 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 B₂O₃ 2.17 2.03 2.41 2.47 2.47 2.46 2.38 1.171.18 1.15 Al₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li₂O0.00 1.66 1.29 1.59 1.33 1.32 0.94 0.67 0.67 0.66 Na₂O 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 K₂O 1.86 2.20 1.63 1.67 1.67 1.671.61 1.06 1.06 1.04 MgO 0.00 0.00 0.00 0.00 0.95 0.00 0.00 0.00 0.000.00 CaO 0.00 0.00 0.00 0.00 0.00 1.32 1.28 1.26 2.53 1.24 SrO 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 BaO 13.07 5.37 5.30 2.71 1.811.81 5.25 3.44 3.45 6.76 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 TiO₂ 9.54 18.64 19.32 19.80 19.84 19.76 19.14 21.04 20.2419.80 Nb₂O₅ 53.37 46.52 45.93 47.06 47.16 46.99 45.50 44.71 44.90 43.94ZrO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi₂O₃ 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 WO₃ 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 Y₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 La₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sb₂O₃0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Li₂O + Na₂O +K₂O + 14.93 9.22 8.22 5.97 5.76 6.11 9.08 6.42 7.71 9.69 MgO + CaO +ZnO + SrO + BaO TiO₂ + Nb₂O₅ 62.91 65.15 65.26 66.85 67.00 66.75 64.6465.75 65.14 63.74 K₂O/ 1.00 0.57 0.56 0.51 0.56 0.56 0.63 0.61 0.61 0.61(Li₂O + Na₂O + K₂O) (MgO + CaO + ZnO + 7.01 1.39 1.82 0.83 0.92 1.052.56 2.72 3.45 4.71 SrO + BaO)/ (Li₂O + Na₂O + K₂O) TiO₂/K₂O 5.12 8.4811.87 11.87 11.87 11.87 11.87 19.92 19.08 19.08 (Li₂O + Na₂O + MgO +0.00 0.22 0.19 0.36 0.65 0.76 0.32 0.43 0.71 0.24 CaO + ZnO + SrO)/(K₂O + BaO) nd 2.0012 1.99678 1.99804 1.99825 1.99591 1.99759 1.996381.99669 1.99601 1.99573 νd 18.07 17.49 17.4 17.28 17.34 17.37 17.5517.18 17.46 17.5 Specific gravity 3.912 3.627 3.605 3.549 3.537 3.5513.624 3.553 3.587 3.636 Tg 678 625 612 614 610 614 626 642 644 643 λ70514 508 509 507 509 506 503 503 491 511 λ5 393 397 397 396 396 396 396397 396 397 nd/specific gravity 0.51 0.55 0.55 0.56 0.56 0.56 0.55 0.560.56 0.55 P₂O₅ + TiO₂ + Nb₂O₅ 82.90 88.75 89.38 91.57 91.77 91.42 88.5492.41 91.11 89.16 Li₂O + Na₂O + K₂O 1.86 3.85 2.92 3.25 3.00 2.99 2.551.73 1.73 1.70 SrO + BaO 13.07 5.37 5.30 2.71 1.81 1.81 5.25 3.44 3.456.76 ZnO + SrO + BaO 13.07 5.37 5.30 2.71 1.81 1.81 5.25 3.44 3.45 6.76MgO + CaO + ZnO + 13.07 5.37 5.30 2.71 2.77 3.13 6.53 4.70 5.98 7.99SrO + BaO TiO₂ + Nb₂O₅ + 62.91 65.15 65.26 66.85 67.00 66.75 64.64 65.7565.14 63.74 WO₃ + Bi₂O₃ P₂O₅/ 0.24 0.27 0.27 0.27 0.27 0.27 0.27 0.290.29 0.29 (P₂O₅ + TiO₂ + Nb₂O₅) TiO₂/ 5.12 4.84 6.62 6.08 6.62 6.62 7.5112.19 11.67 11.67 (Li₂O + Na₂O + K₂O) BaO/(MgO + CaO + 1.00 1.00 1.001.00 0.66 0.58 0.80 0.73 0.58 0.85 ZnO + SrO + BaO) TiO₂/(MgO + CaO +0.73 3.47 3.65 7.29 7.17 6.32 2.93 4.48 3.38 2.48 ZnO + SrO + BaO)TiO₂/(TiO₂ + Nb₂O₅) 0.15 0.29 0.30 0.30 0.30 0.30 0.30 0.32 0.31 0.31TiO₂/(TiO₂ + Nb₂O₅ + 0.15 0.29 0.30 0.30 0.30 0.30 0.30 0.32 0.31 0.31WO₃ + Bi₂O₃) TiO₂/Nb₂O₅ 0.18 0.40 0.42 0.42 0.42 0.42 0.42 0.47 0.450.45 TiO₂/(Nb₂O₅ + 0.18 0.40 0.42 0.42 0.42 0.42 0.42 0.47 0.45 0.45WO₃ + Bi₂O₃) (TiO₂ + Nb₂O₅)/ 3.68 5.79 6.14 7.93 8.14 7.78 5.64 8.667.33 5.88 (SiO₂ + B₂O₃ + Li₂O + Na₂O + K₂O + MgO + CaO + ZnO + SrO +BaO) Sample 31 32 33 34 35 36 37 38 39 40 P₂O₅ 26.74 26.01 25.92 25.9726.04 26.33 27.42 26.67 26.97 26.33 SiO₂ 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 B₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 Al₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li₂O 0.670.67 0.50 0.67 0.67 0.68 0.67 0.67 0.68 0.50 Na₂O 0.70 0.70 0.70 0.350.70 0.71 0.35 0.70 0.70 0.69 K₂O 2.12 2.66 3.18 3.18 3.19 3.23 2.112.11 2.14 2.61 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 CaO1.26 1.26 1.26 1.26 0.63 1.28 1.26 0.63 1.27 1.24 SrO 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 BaO 3.45 3.46 3.45 3.45 3.46 1.753.43 3.44 1.74 3.40 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 TiO₂ 20.21 20.27 20.19 20.23 20.29 20.51 20.12 21.05 21.29 18.13Nb₂O₅ 44.85 44.97 44.80 44.89 45.01 45.51 44.65 44.73 45.22 47.10 ZrO₂0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi₂O₃ 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 WO₃ 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 Y₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 La₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sb₂O₃ 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 Li₂O + Na₂O + K₂O +8.20 8.75 9.08 8.92 8.66 7.65 7.82 7.55 6.53 8.43 MgO + CaO + ZnO +SrO + BaO TiO₂ + Nb₂O₅ 65.06 65.23 65.00 65.12 65.30 66.02 64.77 65.7866.51 65.24 K₂O/ 0.61 0.66 0.73 0.76 0.70 0.70 0.67 0.61 0.61 0.69(Li₂O + Na₂O + K₂O) (MgO + CaO + ZnO + 1.35 1.17 1.08 1.12 0.90 0.661.50 1.17 0.86 1.22 SrO + BaO)/ (Li₂O + Na₂O + K₂O) TiO₂/K₂O 9.54 7.636.36 6.36 6.36 6.36 9.54 9.96 9.96 6.95 (Li₂O + Na₂O + MgO + 0.47 0.430.37 0.34 0.30 0.54 0.41 0.36 0.68 0.40 CaO + ZnO + SrO)/ (K₂O + BaO) nd1.98902 1.99117 1.98766 1.98934 1.98901 1.98899 1.9873 1.99523 1.995221.98749 νd 17.25 17.25 17.3 17.3 17.21 17.2 17.28 17.08 17.06 17.33Specific gravity 3.564 3.574 3.567 3.569 3.566 3.537 3.551 3.561 3.5343.579 Tg 651 652 657 654 657 654 655 652 652 661 λ70 510 500 498 500 503501 502 502 499 498 λ5 398 397 397 398 398 398 397 397 397 397nd/specific gravity 0.56 0.56 0.56 0.56 0.56 0.56 0.56 0.56 0.56 0.56P₂O₅ + TiO₂ + Nb₂O₅ 91.80 91.25 90.92 91.08 91.34 92.35 92.18 92.4593.47 91.57 Li₂O + Na₂O + K₂O 3.49 4.03 4.38 4.20 4.56 4.62 3.13 3.483.52 3.79 SrO + BaO 3.45 3.46 3.45 3.45 3.46 1.75 3.43 3.44 1.74 3.40ZnO + SrO + BaO 3.45 3.46 3.45 3.45 3.46 1.75 3.43 3.44 1.74 3.40 MgO +CaO + ZnO + 4.71 4.72 4.71 4.71 4.10 3.03 4.69 4.07 3.01 4.64 SrO + BaOTiO₂ + Nb₂O₅ + 65.06 65.23 65.00 65.12 65.30 66.02 64.77 65.78 66.5165.24 WO₃ + Bi₂O₃ P₂O₅/ 0.29 0.29 0.29 0.29 0.29 0.29 0.30 0.29 0.290.29 (P₂O₅ + TiO₂ + Nb₂O₅) TiO₂/ 5.79 5.03 4.61 4.81 4.44 4.44 6.44 6.056.05 4.78 (Li₂O + Na₂O + K₂O) BaO/(MgO + CaO + 0.73 0.73 0.73 0.73 0.850.58 0.73 0.85 0.58 0.73 ZnO + SrO + BaO) TiO₂/(MgO + CaO + 4.29 4.294.29 4.29 4.95 6.77 4.29 5.17 7.07 3.91 ZnO + SrO + BaO) TiO₂/(TiO₂ +Nb₂O₅) 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.32 0.32 0.28 TiO₂/(TiO₂ +Nb₂O₅ + 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.32 0.32 0.28 WO₃ + Bi₂O₃)TiO₂/Nb₂O₅ 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.47 0.47 0.38TiO₂/(Nb₂O₅ + 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.47 0.47 0.38 WO₃ +Bi₂O₃) (TiO₂ + Nb₂O₅)/ 7.93 7.45 7.16 7.30 7.54 8.64 8.29 8.71 10.197.74 (SiO₂ + B₂O₃ + Li₂O + Na₂O + K₂O + MgO + CaO + ZnO + SrO + BaO)

TABLE 3 Sample 41 42 43 44 45 46 47 48 49 50 P₂O₅ 26.97 27.01 26.6727.26 26.67 26.99 26.11 26.06 25.76 25.84 SiO₂ 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 B₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 Al₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li₂O0.51 0.42 0.41 0.42 0.08 0.08 0.08 0.08 0.08 0.08 Na₂O 0.70 1.04 0.680.70 0.69 0.69 0.67 0.67 0.66 0.00 K₂O 2.67 2.11 2.60 2.66 3.12 3.163.06 3.05 3.02 3.03 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 CaO 1.27 1.26 0.62 1.90 1.24 1.25 0.00 1.21 1.20 0.00 SrO 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 BaO 3.48 3.43 5.08 1.73 3.393.43 6.64 3.31 3.27 6.57 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 TiO₂ 22.19 20.11 19.86 20.30 20.74 22.78 20.31 16.82 14.9221.80 Nb₂O₅ 42.21 44.63 44.07 45.03 44.07 41.62 43.14 48.80 51.08 42.69ZrO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi₂O₃ 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 WO₃ 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 Y₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 La₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sb₂O₃0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Li₂O + Na₂O +K₂O + 8.63 8.25 9.40 7.41 8.52 8.62 10.44 8.32 8.23 9.67 MgO + CaO +ZnO + SrO + BaO TiO₂ + Nb₂O₅ 64.40 64.74 63.93 65.33 64.81 64.39 63.4565.62 66.01 64.49 K₂O/ 0.69 0.59 0.70 0.70 0.80 0.80 0.80 0.80 0.80 0.97(Li₂O + Na₂O + K₂O) (MgO + CaO + ZnO + 1.22 1.31 1.54 0.96 1.19 1.191.74 1.19 1.19 2.11 SrO + BaO)/ (Li₂O + Na₂O + K₂O) TiO₂/K₂O 8.3 9.547.63 7.63 6.64 7.21 6.64 5.51 4.95 7.21 (Li₂O + Na₂O + MgO + 0.40 0.490.22 0.69 0.31 0.31 0.08 0.31 0.31 0.01 CaO + ZnO + SrO)/ (K₂O + BaO) nd1.98681 1.98621 1.98504 1.98423 1.98569 1.98517 1.9855 1.98616 1.986371.99599 νd 17.23 17.29 17.32 17.29 17.2 17.15 17.26 17.3 17.45 17.04Specific gravity 3.543 3.559 3.583 3.529 3.546 3.533 3.606 3.586 3.6113.602 Tg 658 668 670 650 673 673 687 684 689 685 λ70 503 489 493 492 490499 497 513 504 497 λ5 398 397 397 397 397 398 397 397 395 398nd/specific gravity 0.56 0.56 0.55 0.56 0.56 0.56 0.55 0.55 0.55 0.55P₂O₅ + TiO₂ + Nb₂O₅ 91.37 91.75 90.60 92.59 91.48 91.38 89.56 91.6891.77 90.33 Li₂O + Na₂O + K₂O 3.88 3.57 3.70 3.78 3.89 3.94 3.81 3.803.76 3.11 SrO + BaO 3.48 3.43 5.08 1.73 3.39 3.43 6.64 3.31 3.27 6.57ZnO + SrO + BaO 3.48 3.43 5.08 1.73 3.39 3.43 6.64 3.31 3.27 6.57 MgO +CaO + ZnO + 4.75 4.69 5.70 3.63 4.63 4.68 6.64 4.52 4.47 6.57 SrO + BaOTiO₂ + Nb₂O₅ + 64.40 64.74 63.93 65.33 64.81 64.39 63.45 65.62 66.0164.49 WO₃ + Bi₂O₃ P₂O₅/ 0.30 0.29 0.29 0.29 0.29 0.30 0.29 0.28 0.280.29 (P₂O₅ + TiO₂ + Nb₂O₅) TiO₂/ 5.72 5.64 5.37 5.37 5.33 5.79 5.33 4.423.97 7.02 (Li₂O + Na₂O + K₂O) BaO/(MgO + CaO + 0.73 0.73 0.89 0.48 0.730.73 1.00 0.73 0.73 1.00 ZnO + SrO + BaO) TiO₂/(MgO + CaO + 4.67 4.293.48 5.59 4.48 4.86 3.06 3.72 3.34 3.32 ZnO + SrO + BaO) TiO₂/(TiO₂ +Nb₂O₅) 0.34 0.31 0.31 0.31 0.32 0.35 0.32 0.26 0.23 0.34 TiO₂/(TiO₂ +Nb₂O₅ + 0.34 0.31 0.31 0.31 0.32 0.35 0.32 0.26 0.23 0.34 WO₃ + Bi₂O₃)TiO₂/Nb₂O₅ 0.53 0.45 0.45 0.45 0.47 0.55 0.47 0.34 0.29 0.51TiO₂/(Nb₂O₅ + 0.53 0.45 0.45 0.45 0.47 0.55 0.47 0.34 0.29 0.51 WO₃ +Bi₂O₃) (TiO₂ + Nb₂O₅)/ 7.46 7.84 6.80 8.81 7.61 7.47 6.07 7.88 8.02 6.67(SiO₂ + B₂O₃ + Li₂O + Na₂O + K₂O + MgO + CaO + ZnO + SrO + BaO) Sample51 52 53 54 55 56 57 58 59 60 P₂O₅ 25.55 24.89 25.26 25.84 25.44 25.3325.40 25.32 25.24 25.26 SiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.320.63 0.00 B₂O₃ 0.00 0.37 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Al₂O₃0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li₂O 0.08 0.08 0.080.08 0.08 0.08 0.01 0.01 0.01 0.08 Na₂O 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 K₂O 2.99 3.00 2.47 3.53 2.98 2.97 2.97 2.97 2.962.96 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 CaO 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 SrO 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 BaO 6.49 6.52 8.03 4.92 5.66 4.83 6.46 6.446.42 6.42 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 TiO₂19.87 19.95 19.65 20.09 19.79 19.70 19.76 19.70 19.63 19.65 Nb₂O₅ 45.0245.20 44.52 45.53 44.84 44.65 45.40 45.26 45.12 45.63 ZrO₂ 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi₂O₃ 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 WO₃ 0.00 0.00 0.00 0.00 1.22 2.43 0.00 0.000.00 0.00 Y₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 La₂O₃0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sb₂O₃ 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 Li₂O + Na₂O + K₂O + 9.56 9.6010.57 8.53 8.72 7.87 9.44 9.41 9.38 9.46 MgO + CaO + ZnO + SrO + BaOTiO₂ + Nb₂O₅ 64.89 65.14 64.17 65.63 64.62 64.36 65.16 64.95 64.75 65.28K₂O/ 0.97 0.97 0.97 0.98 0.97 0.97 1.00 1.00 1.00 0.97 (Li₂O + Na₂O +K₂O) (MgO + CaO + ZnO + 2.11 2.11 3.16 1.36 1.85 1.59 2.16 2.16 2.162.11 SrO + BaO)/ (Li₂O + Na₂O + K₂O) TiO₂/K₂O 6.64 6.64 7.97 5.69 6.646.64 6.64 6.64 6.64 6.64 (Li₂O + Na₂O + MgO + 0.01 0.01 0.01 0.01 0.010.01 0.00 0.00 0.00 0.01 CaO + ZnO + SrO)/ (K₂O + BaO) nd 1.9963 1.999761.99824 1.99398 1.99781 1.99968 1.99718 1.99469 1.99171 1.99933 νd 17.0817.06 17.17 17.01 16.99 16.91 17.06 17.14 17.19 17.04 Specific gravity3.628 3.633 3.668 3.589 3.63 3.633 3.633 3.626 3.619 3.637 Tg 687 677695 683 687 687 690 693 693 688 λ70 497 526 506 507 569 527 504 514 492522 λ5 397 399 398 398 401 401 399 399 398 399 nd/specific gravity 0.550.55 0.54 0.56 0.55 0.55 0.55 0.55 0.55 0.55 P₂O₅ + TiO₂ + Nb₂O₅ 90.4490.03 89.43 91.47 90.06 89.69 90.56 90.28 89.99 90.54 Li₂O + Na₂O + K₂O3.07 3.08 2.54 3.61 3.06 3.05 2.98 2.97 2.96 3.04 SrO + BaO 6.49 6.528.03 4.92 5.66 4.83 6.46 6.44 6.42 6.42 ZnO + SrO + BaO 6.49 6.52 8.034.92 5.66 4.83 6.46 6.44 6.42 6.42 MgO + CaO + ZnO + 6.49 6.52 8.03 4.925.66 4.83 6.46 6.44 6.42 6.42 SrO + BaO TiO₂ + Nb₂O₅ + 64.89 65.14 64.1765.63 65.85 66.79 65.16 64.95 64.75 65.28 WO₃ + Bi₂O₃ P₂O₅/ 0.28 0.280.28 0.28 0.28 0.28 0.28 0.28 0.28 0.28 (P₂O₅ + TiO₂ + Nb₂O₅) TiO₂/ 6.476.47 7.72 5.57 6.47 6.47 6.62 6.62 6.62 6.47 (Li₂O + Na₂O + K₂O)BaO/(MgO + CaO + 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 ZnO +SrO + BaO) TiO₂/(MgO + CaO + 3.06 3.06 2.45 4.08 3.50 4.08 3.06 3.063.06 3.06 ZnO + SrO + BaO) TiO₂/(TiO₂ + Nb₂O₅) 0.31 0.31 0.31 0.31 0.310.31 0.30 0.30 0.30 0.30 TiO₂/(TiO₂ + Nb₂O₅ + 0.31 0.31 0.31 0.31 0.300.30 0.30 0.30 0.30 0.30 WO₃ + Bi₂O₃) TiO₂/Nb₂O₅ 0.44 0.44 0.44 0.440.44 0.44 0.44 0.44 0.44 0.43 TiO₂/(Nb₂O₅ + 0.44 0.44 0.44 0.44 0.430.42 0.44 0.44 0.44 0.43 WO₃ + Bi₂O₃) (TiO₂ + Nb₂O₅)/ 6.79 6.53 6.077.69 7.41 8.17 6.90 6.68 6.47 6.90 (SiO₂ + B₂O₃ + Li₂O + Na₂O + K₂O +MgO + CaO + ZnO + SrO + BaO)

TABLE 4 Sample 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 P₂O₅ 24.0425.05 25.33 25.12 24.91 25.77 24.49 24.58 26.45 24.72 25.63 25.41 25.4825.28 25.35 SiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 B₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 1.62 1.63 1.651.64 0.00 0.00 0.00 0.00 0.00 Al₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li₂O 0.08 0.08 0.08 0.08 0.080.08 0.00 0.00 0.00 0.00 0.08 0.08 0.08 0.08 0.08 Na₂O 0.00 0.00 0.000.00 0.00 0.00 1.90 2.61 1.93 1.92 0.00 0.00 0.00 0.00 0.00 K₂O 3.152.93 2.97 2.21 2.92 3.02 4.15 3.11 4.21 4.19 3.50 2.73 2.74 2.71 2.72MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 CaO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.001.17 0.00 0.00 0.00 0.00 0.00 BaO 2.21 6.37 6.44 8.78 6.33 6.55 8.368.39 8.47 8.43 6.52 6.46 6.48 6.43 6.44 ZnO 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.92 0.00 0.00 0.00 0.00 0.00 TiO₂ 24.77 19.48 20.5419.54 17.71 23.49 15.14 15.19 15.35 15.28 19.09 19.34 19.82 19.24 19.72Nb₂O₅ 30.24 46.08 44.65 44.28 48.05 41.10 44.34 44.49 41.94 41.73 45.1844.79 44.21 44.55 43.98 ZrO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi₂O₃ 4.80 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 WO₃ 10.72 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Y₂O₃ 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.19 1.19 0.00 0.00 La₂O₃0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.711.71 Sb₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Li₂O + Na₂O +K₂O + 5.44 9.38 9.48 11.06 9.33 9.65 14.41 14.11 14.61 15.71 10.10 9.279.30 9.22 9.24 MgO + CaO + ZnO + SrO + BaO TiO₂ + Nb₂O₅ 55.01 65.5765.19 63.82 65.76 64.59 59.48 59.68 57.29 57.01 64.27 64.13 64.03 63.7963.70 K₂O/ 0.98 0.97 0.97 0.97 0.97 0.97 0.69 0.54 0.69 0.69 0.98 0.970.97 0.97 0.97 (Li₂O + Na₂O + K₂O) (MgO + CaO + ZnO + 0.68 2.11 2.113.84 2.11 2.11 1.38 1.47 1.38 1.72 1.82 2.30 2.30 2.30 2.30 SrO + BaO)/(Li₂O + Na₂O + K₂O) TiO₂/K₂O 7.86 6.64 6.92 8.86 6.07 7.78 3.65 4.883.65 3.65 5.45 7.08 7.23 7.10 7.25 (Li₂O + Na₂O + MgO + 0.01 0.01 0.010.01 0.01 0.01 0.15 0.23 0.15 0.32 0.01 0.01 0.01 0.01 0.01 CaO + ZnO +SrO)/ (K₂O + BaO) nd 2.01368 2.00182 2.00002 1.99973 2.00047 1.999621.95054 1.95348 1.93138 1.93778 1.98938 1.99394 1.99392 1.99625 1.99622νd 16.43 17.02 17.02 17.2 17.1 16.94 18.31 18.26 18.67 18.76 17.21 17.317.27 17.28 17.28 Specific gravity 3.754 3.645 3.632 3.69 3.653 3.5973.632 3.641 3.584 3.65 3.616 3.643 3.639 3.699 3.666 Tg 641 689 681 693690 680 667 665 681 641 695 684 685 696 685 λ70 534 530 503 496 518 509479 484 474 480 497 499 504 505 499 λ5 409 399 399 399 398 400 394 394394 393 398 398 398 398 398 nd/specific gravity 0.54 0.55 0.55 0.54 0.550.56 0.54 0.54 0.54 0.53 0.55 0.55 0.55 0.54 0.54 P₂O₅ + TiO₂ + Nb₂O₅79.05 90.62 90.52 88.94 90.67 90.35 83.97 84.26 83.74 81.73 89.90 89.5489.51 89.07 89.05 Li₂O + Na₂O + K₂O 3.23 3.01 3.04 2.28 2.99 3.10 6.055.72 6.14 6.11 3.58 2.81 2.82 2.79 2.80 SrO + BaO 2.21 6.37 6.44 8.786.33 6.55 8.36 8.39 8.47 9.60 6.52 6.46 6.48 6.43 6.44 ZnO + SrO + BaO2.21 6.37 6.44 8.78 6.33 6.55 8.36 8.39 8.47 10.52 6.52 6.46 6.48 6.436.44 MgO + CaO + ZnO + 2.21 6.37 6.44 8.78 6.33 6.55 8.36 8.39 8.4710.52 6.52 6.46 6.48 6.43 6.44 SrO + BaO TiO₂ + Nb₂O₅ + 70.52 65.5765.19 63.82 65.76 64.59 59.48 59.68 57.29 57.01 64.27 64.13 64.03 63.7963.70 WO₃ + Bi₂O₃ P₂O₅/ 0.30 0.28 0.28 0.28 0.27 0.29 0.29 0.29 0.320.30 0.29 0.28 0.28 0.28 0.28 (P₂O₅ + TiO₂ + Nb₂O₅) TiO₂/ 7.67 6.47 6.758.55 5.91 7.58 2.50 2.66 2.50 2.50 5.33 6.88 7.03 6.90 7.04 (Li₂O +Na₂O + K₂O) BaO/(MgO + CaO + 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.001.00 0.80 1.00 1.00 1.00 1.00 1.00 ZnO + SrO + BaO) TiO₂/(MgO + CaO +11.21 3.06 3.19 2.23 2.80 3.59 1.81 1.81 1.81 1.45 2.93 2.99 3.06 2.993.06 ZnO + SrO + BaO) TiO₂/(TiO₂ + Nb₂O₅) 0.45 0.30 0.32 0.31 0.27 0.360.25 0.25 0.27 0.27 0.30 0.30 0.31 0.30 0.31 TiO₂/(TiO₂ + Nb₂O₅ + 0.350.30 0.32 0.31 0.27 0.36 0.25 0.25 0.27 0.27 0.30 0.30 0.31 0.30 0.31WO₃ + Bi₂O₃) TiO₂/Nb₂O₅ 0.82 0.42 0.46 0.44 0.37 0.57 0.34 0.34 0.370.37 0.42 0.43 0.45 0.43 0.45 TiO₂/(Nb₂O₅ + 0.54 0.42 0.46 0.44 0.370.57 0.34 0.34 0.37 0.37 0.42 0.43 0.45 0.43 0.45 WO₃ + Bi₂O₃) (TiO₂ +Nb₂O₅)/ 10.11 6.99 6.87 5.77 7.05 6.70 3.71 3.79 3.52 3.29 6.36 6.926.88 6.92 6.89 (SiO₂ + B₂O₃ + Li₂O + Na₂O + K₂O + MgO + CaO + ZnO +SrO + BaO)

Example 2

A lens blank was prepared by a known method by using each optical glassprepared in Example 1, and the lens blank was processed by a knownmethod such as polishing to prepare various lenses.

The prepared optical lenses are various lenses such as a planar lens, abiconvex lens, a biconcave lens, a plano-convex lens, a plano-concavelens, a concave meniscus lens, and a convex meniscus lens.

When the various lenses are combined with a lens formed from anotherkind of optical glass, secondary chromatic aberration can be correctedin a satisfactory manner.

In addition, since the glass has a low specific gravity, each of thelenses is lighter in weight in comparison to a lens having the sameoptical properties and the same size, and is suitable for a goggle-typeor eyeglass-type AR display device or MR display device. In the samemanner, a prism was prepared by using the various kinds of optical glassprepared in Example 1.

Example 3

Each optical glass prepared in Example 1 was processed into arectangular shape having dimensions of 50 mm (length)×20 mm (width)×1.0mm (thickness), thereby obtaining a light guide plate. The light guideplate was assembled into the head-mounted display 1 illustrated in FIG.1 .

With respect to the head-mounted display obtained in this manner, animage was evaluated at a position of an eye point. From the evaluation,an image with a high luminance and a high contrast could be observed ata wide viewing angle.

It should be considered that the disclosed embodiment is illustrativeonly in all aspects, and is not restrictive. The scope of the presentinvention is represented by the accompanying claims rather than theabove description, and is intended to include meaning equivalent to theaccompanying claims and all modifications in the claims.

For example, the optical glass according to the aspect of the presentinvention can be prepared by performing an adjustment of the compositiondescribed in this specification with respect to the exemplified glasscompositions.

In addition, two or more of the matters which are exemplified in thisspecification or described as preferable ranges may be combined in anarbitrary manner.

What is claimed is:
 1. Optical glass, wherein an amount of P₂O₅ is 10.0to 40.0 mass %, an amount of TiO₂ is 5.0 to 40.0 mass %, an amount ofNb₂O₅ is 20.0 to 60.0 mass %, an amount of K₂O is 0.01 mass % or more, atotal amount of Li₂O, Na₂O, K₂O, MgO, CaO, ZnO, SrO, and BaO[Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is 20.0 mass % or less, a totalamount of TiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] is 55.0 mass % or more, a massratio [K₂O/(Li₂O+Na₂O+K₂O)] between the amount of K₂O, and a totalamount of Li₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is 0.5 or more, a massratio [(MgO+CaO+ZnO+SrO+BaO)/(Li₂O+Na₂O+K₂O)] between a total amount ofMgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO], and the total amountof Li₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is 0.30 to 10.0, a mass ratio[TiO₂/K₂O] between the amount of TiO₂ and the amount of K₂O is 3.0 ormore, and a mass ratio [(Li₂O+Na₂O+MgO+CaO+ZnO+SrO)/(K₂O+BaO)] between atotal amount of Li₂O, Na₂O, MgO, CaO, ZnO, and SrO[Li₂O+Na₂O+MgO+CaO+ZnO+SrO], and a total amount of K₂O and BaO [K₂O+BaO]is 0.8 or less.
 2. The optical glass according to claim 1, wherein amass ratio [(TiO₂+Nb₂O₅)/(SiO₂+B₂O₃+Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO)]between the total amount of TiO₂ and Nb₂O₅[TiO₂+Nb₂O₅] and a totalamount of SiO₂, B₂O₃, Li₂O, Na₂O, K₂O, MgO, CaO, ZnO, SrO, and BaO[SiO₂+B₂O₃+Li₂O+Na₂O+K₂O+MgO+CaO+ZnO+SrO+BaO] is 2.65 or more.
 3. Theoptical glass according to claim 1, a total amount of TiO₂, Nb₂O₅, WO₃,and Bi₂O₃[TiO₂+Nb₂O₅+WO₃+Bi₂O₃] is 40.0 to 80.0 mass %.
 4. The opticalglass according to claim 1, wherein a mass ratio[P₂O₅/(P₂O₅+TiO₂+Nb₂O₅)] between the amount of P₂O₅ and a total amountof P₂O₅, TiO₂, and Nb₂O₅[P₂O₅+TiO₂+Nb₂O₅] is 0.15 to 0.40.
 5. Theoptical glass according to claim 1, wherein a mass ratio[TiO₂/([Li₂O+Na₂O+K₂O])] between the amount of TiO₂ and the total amountof Li₂O, Na₂O, and K₂O [Li₂O+Na₂O+K₂O] is 1.0 to 30.0.
 6. The opticalglass according to claim 1, wherein a mass ratio[BaO/([MgO+CaO+ZnO+SrO+BaO])] between an amount of BaO and the totalamount of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] is 0 ormore.
 7. The optical glass according to claim 1, wherein a mass ratio[TiO₂/(MgO+CaO+ZnO+SrO+BaO)] between the amount of TiO₂ and the totalamount of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] is 0.1 to50.0.
 8. The optical glass according to claim 1, wherein a mass ratio[TiO₂/(TiO₂+Nb₂O₅+WO₃+Bi₂O₃)] between the amount of TiO₂ and a totalamount of TiO₂, Nb₂O₅, WO₃, and Bi₂O₃ is 0.10 to 0.60.
 9. The opticalglass according to claim 1, where in a refractive index nd is 1.950 ormore.
 10. The optical glass according to claim 1, wherein an Abbe numbervd is 15.0 to 20.0.
 11. The optical glass according to claim 1, whereina specific gravity is 4.20 or less.
 12. The optical glass according toclaim 1, wherein a ratio [nd/d] between a refractive index nd and aspecific gravity d is 0.48 to 0.60.
 13. The optical glass according toclaim 1, wherein a glass transition temperature Tg is 380° C. to 800° C.14. An optical element blank comprising the optical glass according toclaim
 1. 15. An optical element blank comprising the optical glassaccording to claim
 2. 16. An optical element comprising the opticalglass according to claim
 1. 17. An optical element comprising theoptical glass according to claim 2.